Activated ras oncogenes have been identified in a significant percentage of cancers including leukemias and carcinomas of the colon, pancreas and lung. High affinity antibodies reactive with both normal and activated human p21ras are available. However, previous attempts to develop antibodies specific for mutant p21ras, by use of synthetic peptide immunogens, have not produced reagents of sufficient quality for clinical diagnostic assays. In order to obtain improved antibodies against activated ras proteins, recombinant p21ras protein, encoded by a K-ras gene with a mutation causing an aspartic acid for glycine substitution at residue 12, will be used to immunize rabbits. The desired antibodies will be purified by affinity chromatography on mutant p21ras, and antibodies reactive with normal ras proteins will be removed by absorption against wild-type p21ras. The antibodies will be assessed for binding to mutationally activated p21ras proteins, and will be used to develop both immunometric (antigen capture) and immunohistochemical assays for the mutant proteins. The ability to rapidly identify activated p21ras proteins in tumor biopsy specimens will greatly facilitate the progress of research on the clinical significance of ras oncogene activation, and should improve the specific diagnosis and prognostic evaluation of human cancer.